1. Field of the Invention
This invention relates to signal transmission systems and more particularly to systems for transmitting and receiving modulated rays of electromagnetic radiation, such as visible light or near visible light.
2. Description of the Related Art
The art of light communication between distant points is old. The fundamental goal in this art is to use light to effect a transfer of data from a data source to a data destination. It is well known that light communications in a controlled medium such as a fiber optic disc can yield high data throughput rates. Accordingly, there exists a significant amount of disclosure in the prior art relating to fiber optic communications devices and systems. Because the fiber optic cable can be used to conduct beams of light, the path of the light beams as well as their diminishing intensity due to divergence can be controlled. By some estimates, a fiber optic cable can carry approximately 40 times more information than can a standard electric cable.
Without question, transmission of data optically versus by wire means is becoming more and more prevalent. Numerous reasons exist for preferring optical transmission of data, as opposed to electrical transmission. These reasons include less bandwidth limitations, lack of electrical interference, reduced weight, and reduced bulk. Optical data transmission can provide huge bandwidth characteristics, extremely low loss even over long distances and immunity to electrical interference even in environments saturated with electronics such as aircrafts. Resultingly, light based communications and even data storage devices are under wide scale development.
Given the amount of cabling that current office and home environments must have in order to provide power, voice carrying capabilities, data carrying capabilities, etc., there is a need to reduce the amount of cabling to facilitate movement of equipment, aesthetics, and even safety. Accordingly, cableless electromagnetic communications systems and especially light based communications systems seem to offer potential for carrying signals with sufficient throughput capability for handling voice information and data.
As fiber optic technologies have evolved, cableless data transmission systems based upon light signals have also been pursued. Some references teach that "wireless" or cableless remote controls may utilize infrared transmitters and receivers to relay information relating to user selected options, e.g., the remote control for the television. Thus, infrared communications devices are already being employed for devices which do not have high data throughputs, e.g. remote controls for stereo and television equipment. Such devices produce a wide angle diverging signal which reaches its destination infrared receiver because of the relatively low frequency or long period of its signals and because of the lenses used for such transmitters. Such lenses allow the light beams to diverge in order to insure that a signal is received by the infrared receiver without absolute precision in aim.
A drawback, however, to such systems for data transfer is that low frequency signals must be used because of the divergent characteristic of emitted beam. The range of a light beam, for data transfer purposes, is proportional to its density. Therefore, a diverging light beam pattern will have shorter range capabilities. By some estimates, the luminous intensity of light is ten times greater with a narrow beam than with a wide beam. Thus, a narrow beam has a range that is over 3 times longer (square root of ten--the difference in intensity). Thus, it has been recognized that data throughput rates may be increased by focusing the light beam to produce a relatively non-divergent beam of light. A problem with use of focused beams, however, is that precise aim must be used, especially for long range transmissions, in order for the signal to illuminate the infrared receiver. Additionally, the beam of light may easily be momentarily blocked by a object moving through its path. Thus, data transfer is interrupted and perhaps either terminated or at least degraded.